1. Field of the Invention
The present invention relates to an image insertion device for compressed video data, by which a logo image is inserted into video data with a high speed and high efficiency.
2. Description of the Related Art
As a previous method for inserting an image into compressed video data, there is, for example, an image insertion method at a base band, as shown in FIG. 11. Hereinafter, operations in the previous method will be explained. In the first place, a decoder 101 decodes all data in one frame of MPEG compressed data as an input signal. Then, an image 103 to be inserted is inserted into the decoded image in a combiner 102 to be recompressed in an encoder 104. In this case, coding information (p) of input data which has been decoded in the decoder 101, for example, information such as moving information MV and encoding type is sent to the encoder 104 and is used for encoding. MPEG data after the image was inserted is output from the encoder 104.
Though an image 103 such as an logo image can be inserted into the input video without almost causing image degradation according to the previous method, there has been a very large problem that an entire amount of processing is large and the processing cost is large even if the coding information (p) on input video is used, because encoding is executed again in the encoder 104.
As another previous method for inserting an image, a method by which a logo image is inserted on the compressed data has been disclosed, for example, in the Japanese Patent Application Publication No. 2001-268572. The method comprises: a step for receiving encoded bit-stream; a step for partially decoding the bit stream; a step for inserting a visual element into the bit stream which has been partially decoded; a step for recoding the bit stream into which the visual element has been inserted; and a step for outputting the recoded bit-stream.
Since the encoded bit-stream is partially decoded according to the method, the entire amount of processing can be reduced.
However, when a logo insertion frame is started from a bidirectionally predictive-coded frame (B frame) in the previous method by which the logo image is inserted on the compressed data, there is a possibility that an encoding efficiency is reduced, because both of the logo region and the non-logo region of the starting prediction frame are recoded according to an inter-frame prediction method to cause inter-frame encoding of the logo region with a low inter-frame encoding efficiency. Here, the reason why the inter-frame encoding efficiency of the starting frame is low is that the inter-frame correlation of the logo region is very weak because there is no logo in frames before the starting frame.
Moreover, since encoding is executed without depending on the mixing ratio between the logo image and the original one, there is a possibility that the encoding efficiency for the logo image with a high mixing ratio (for example, when a deep logo image is combined) is reduced when encoding according to the inter-frame prediction is used in a similar manner to that of the original video.
Here, when an intra-coded frame, instead of the bidirectionally predictive-coded frame (B frame) of the starting frame, is used in order to solve the above-described problem, there has been a problem that image degradation is caused since intra encoding which requires a large amount of bits is used, in spite of a state in which a distributed amount of bits for the bidirectionally predictive-coded frame is small, therefore the amount of bits required for intra encoding becomes insufficient.